Intra prediction method of chrominance block using luminance sample, and apparatus using same
Disclosed are an intra prediction method of a chrominance block using a luminance sample and an apparatus using the same. An image decoding method comprises the steps of: calculating an intra prediction mode of a chrominance block on the basis of an LM mapping table when the chrominance block uses an LM; and generating a prediction block for the chrominance block on the basis of the calculated intra prediction mode of the chrominance block. When intra prediction mode information of chrominance blocks are decoded, mutually different tables are used depending on whether or not an LM is used, so that encoding and decoding can be performed without an unnecessary waste of bits.
1. A decoding apparatus for image decoding, the apparatus comprising:
an entropy decoder configured to receive a bitstream including index information on an intra chroma prediction mode for a current block;
a predictor configured to determine an intra luma prediction mode for the current block, to derive the intra chroma prediction mode based on the intra luma prediction mode and the index information, and to derive a prediction sample of the current block based on the derived intra chroma prediction mode; and
an adder configured to generate a reconstructed picture based on the prediction sample,
wherein a value of the index information represents one of a first mode value, a second mode value, a third mode value, a fourth mode value, or a fifth mode value, wherein the value of the index information is obtained based on a bin string for the index information,
wherein the bin string is one of bin strings of the first mode value through the fifth mode value, bin strings of the first mode value through the fourth mode value are represented by ‘100’, ‘101’, ‘110’ and ‘111’, respectively and a bin string of the fifth mode value is represented by ‘0’, and
wherein, based on a determination that the value of the index information represents the first mode value,
the intra chroma prediction mode is derived as a planar mode based on a determination that the luma intra prediction mode is not the planar mode, and
the intra chroma prediction mode is derived as a diagonal mode representing a diagonal direction to a top right side based on a determination that the luma intra prediction mode is the planar mode.
2. The apparatus of claim 1 , wherein the fifth mode value represents that the intra chroma prediction mode is same as the intra luma prediction mode.
3. The apparatus of claim 1 , wherein based on a determination that the intra chroma prediction mode is different from the intra luma prediction mode, the first mode value represents a planar mode, the second mode value represents a vertical mode, the third mode value represents a horizontal mode, and the fourth mode value represents a DC mode.
4. The apparatus of claim 1 , wherein, based on a determination that the value of the index information represents the second mode value,
the intra chroma prediction mode is derived as a vertical mode based on a determination that the intra luma prediction mode is not the vertical mode, and
the intra chroma prediction mode is derived as a diagonal mode representing a diagonal direction to a top right side based on a determination that the intra luma prediction mode is the vertical mode.
5. The apparatus of claim 1 , wherein, based on a determination that the value of the index information represents the third mode value,
the intra chroma prediction mode is derived as a horizontal mode based on a determination that the intra luma prediction mode is not the horizontal mode, and
the intra chroma prediction mode is derived as a diagonal mode representing a diagonal direction to a top right side based on a determination that the intra luma prediction mode is the horizontal mode.
6. The apparatus of claim 1 , wherein, based on a determination that the value of the index information represents the fourth mode value,
the intra chroma prediction mode is derived as a DC mode based on a determination that the intra luma prediction mode is not the DC mode, and
the intra chroma prediction mode is derived as a diagonal mode representing a diagonal direction to a top right side based on a determination that the intra luma prediction mode is the DC mode.
7. An encoding apparatus for image encoding, the apparatus comprising:
a predictor configured to determine an intra luma prediction mode for a current block, to determine an intra chroma prediction mode for the current block, and to generate index information on the intra chroma prediction mode based on the intra luma prediction mode and the intra chroma prediction mode; and
an entropy encoder configured to encode image information including the index information on the intra chroma prediction mode to generate a bitstream,
wherein a value of the index information represents one of a first mode value, a second mode value, a third mode value, a fourth mode value, or a fifth mode value, wherein the value of the index information is encoded based on a bin string for the index information,
wherein the bin string is one of bin strings of the first mode value through the fifth mode value, bin strings of the first mode value through the fourth mode value are represented by ‘100’, ‘101’, ‘110’ and ‘111’, respectively and a bin string of the fifth mode value is represented by ‘0’, and
wherein, based on a determination that the value of the index information represents the first mode value,
the intra chroma prediction mode is derived as a planar mode based on a determination that the luma intra prediction mode is not the planar mode, and
the intra chroma prediction mode is derived as a diagonal mode representing a diagonal direction to a top right side based on a determination that the luma intra prediction mode is the planar mode.
8. The apparatus of claim 7 , wherein the fifth mode value represents that the intra chroma prediction mode is same as the intra luma prediction mode.
9. The apparatus of claim 7 , wherein, based on a determination that the intra chroma prediction mode is different from the intra luma prediction mode, the first mode value represents a planar mode, the second mode value represents a vertical mode, the third mode value represents a horizontal mode, and the fourth mode value represents a DC mode.
10. The apparatus of claim 7 , wherein, based on a determination that the value of the index information represents the second mode value,
the intra chroma prediction mode is derived as a vertical mode based on a determination that the intra luma prediction mode is not the vertical mode, and
the intra chroma prediction mode is derived as a diagonal mode representing a diagonal direction to a top right side based on a determination that the intra luma prediction mode is the vertical mode.
11. The apparatus of claim 7 , wherein, based on a determination that the value of the index information represents the third mode value,
the intra chroma prediction mode is derived as a horizontal mode based on a determination that the intra luma prediction mode is not the horizontal mode, and
the intra chroma prediction mode is derived as a diagonal mode representing a diagonal direction to a top right side based on a determination that the intra luma prediction mode is the horizontal mode.
12. The apparatus of claim 7 , wherein, based on a determination that the value of the index information represents the fourth mode value,
the intra chroma prediction mode is derived as a DC mode based on a determination that the intra luma prediction mode is not the DC mode, and
the intra chroma prediction mode is derived as a diagonal mode representing a diagonal direction to a top right side based on a determination that the intra luma prediction mode is the DC mode.
13. A non-transitory decoder-readable storage medium storing a bitstream generated by performing determining an intra luma prediction mode for a current block, determining an intra chroma prediction mode for the current block, generating index information on the intra chroma prediction mode based on the intra luma prediction mode and the intra chroma prediction mode, and encoding image information including the index information on the intra chroma prediction mode to generate the bitstream, wherein a value of the index information represents one of a first mode value, a second mode value, a third mode value, a fourth mode value, or a fifth mode value, wherein the value of the index information is encoded based on a bin string for the index information, wherein the bin string is one of bin strings of the first mode value through the fifth mode value, bin strings of the first mode value through the fourth mode value are represented by ‘100’, ‘101’, ‘110’ and ‘111’, respectively and a bin string of the fifth mode value is represented by ‘0’, and wherein, based on a determination that the value of the index information represents the first mode value, the intra chroma prediction mode is derived as a planar mode based on a determination that the luma intra prediction mode is not the planar mode, and the intra chroma prediction mode is derived as a diagonal mode representing a diagonal direction to a top right side based on a determination that the luma intra prediction mode is the planar mode.